The head of state has made the diversification of the economy the main challenge for the national economy, and as a result of the work done in this regard, the GDP of the non-oil sector has increased 3.4 times over the past 20 years, Prime Minister of Azerbaijan Ali Asadov said as he addressed a conference themed "20 years of unparalleled service to the country, people and statehood" dedicated to the 20th anniversary of President of Azerbaijan Ilham Aliyev's presidency, APA reports.